1. Field of the Invention
The present invention relates to a method and apparatus for color image forming, and more particularly to a method and apparatus for color image forming that is capable of performing a precise synchronization between a toner image forming per color and its overlaying with an improved optical synchronization mechanism.
2. Discussion of the Background
In recent years, a color document is a rapidly growing tendency in offices and as a consequence an image forming apparatus such as a copying machine, a printer, a facsimile machine, etc., is also needed to have a color function. In line with an increasing demand for a high quality and a fast speed in office work, the color image forming apparatus is required for a high image quality and a fast processing speed.
Conventionally, a color image forming apparatus in response to such requirements uses a transfer drum method. The color image forming apparatus is provided with a photosensitive drum for forming different color images thereon one by one, and a transfer drum for holding a transfer sheet and transferring the different color images onto the recording sheet in a form overlaying one to another. Another color image forming apparatus in response to such requirements uses a transfer belt method wherein the color image forming apparatus is provided with at least one photosensitive drum and a transfer belt in place of the transfer drum.
In the color image forming apparatus using the transfer drum method, one color image is formed on the photosensitive drum each time the photosensitive drum makes a turn, and different color images are sequentially formed on the photosensitive drum to sequentially transfer the different color images onto the transfer drum. Thereby, a composite color image is formed on the transfer drum and is then transferred onto a transfer sheet. This color image forming procedure not only takes a relatively long time, but it is complex to improve the process speed. Further, this color image forming has a drawback in which performance of the image transferring is varied depending upon a type of transfer sheets, thus, limiting the type of transfer sheets that are used.
In contrast to the above, the color image forming apparatus using the transfer belt method forms different color images on a plurality of photosensitive drums and transfers the different color images onto the transfer belt in an overlaying form to generate a composite color image on the transfer belt which is then transferred onto a transfer sheet. As an alternative, in the color image forming apparatus having an intermediate transfer belt, the different color images are tentatively transferred onto the intermediate transfer belt in an overlaying form to generate a composite color image which is then transferred onto a transfer sheet. It is possible to improve the process speed in these color image forming procedures using the transfer belt method. In addition, this color image forming method does not limit the type of transfer sheets.
FIG. 1 shows a background color image forming apparatus using the transfer belt method. As shown in FIG. 1, the color image forming apparatus includes a laser diode 100, a laser light detector 101, a polygon mirror 102, a mirror 103, a roller motor 104, a driving roller 105, an intermediate transfer belt 106, a photosensitive drum 107, a development unit 108, a transfer roller 109, supporting rollers 110, 111, 112, and 113, and a drum motor 114.
The laser diode 100 emits a laser light beam L modulated in accordance with specific color image data. The polygon mirror 102 is rotated by a polygon motor (not shown) to deflect the laser light beam L. The laser light detector 101 detects the laser light as a scan sync signal each time the laser light beam L completes a line scanning motion. The mirror 103 deflects the laser light beam L towards the photosensitive drum 107. The roller motor 104 drives the driving roller 105 to rotate the intermediate transfer belt 106 which is supported by the transfer roller 109 and the supporting rollers 110-113 to partly contact with the photosensitive drum 107, as shown in FIG. 1. The photosensitive drum 107 has a photosensitive surface and is driven by the drum motor 114.
By exposure to the modulated laser light beam L, an electrostatic latent image for a specific color is formed on the photosensitive surface of the photosensitive drum 107. The development unit 108 includes development assemblies 108a, 108b, 108c, and 108d for containing cyan (C), magenta (M), yellow (Y), and black (K) color toners and developing the electrostatic latent image with a corresponding color toner to form a specific color toner image on the photosensitive drum 107. The transfer roller 109 receives a bias voltage from a power source (not shown) and transfers with the bias voltage the specific color toner image formed on the photosensitive drum 107 onto the intermediate transfer belt 106. Formation of specific color toner image on the photosensitive drum 107 is repeated for the colors of C, M, Y, and B, and the formed color images are in turn transferred onto the intermediate transfer belt 106 in a form of overlaying one to another. Thereby, a composite color toner image is formed on the intermediate transfer belt 106. The composite color toner image thus formed is transferred onto a recording sheet with a secondary transfer mechanism (not shown). Consequently, a final color image is formed on the recording sheet.
The above-described color image forming apparatus controls the drum motor 114 to drive the photosensitive drum 107 in a precise manner so as to control a position of toner image forming to be precisely constant on the surface of the photosensitive drum 107. However, it is not easy to avoid variations in this position due to various factors such as, for example, a manufacturing error in the photosensitive drum itself, a displacement of a mounting position, and so on. As a result, the position of toner image forming is varied, and the background color image forming apparatus fails to form a high precision multi-color toner image.
Furthermore, a problem is encountered on the overlaying images on the intermediate transfer belt 106. That is, the image transfer to the intermediate transfer belt 106 takes place one color image after another color image. Therefore, image transferring needs to be synchronized with the rotation of the photosensitive drum 107, and the synchronization should be controlled in a precise manner. This synchronization is generally performed with a marking/marker provided to an edge of the intermediate transfer belt 106. By reading this marking, a signal is generated to represent a timing that the intermediate transfer belt 106 starts its rotation. With this signal, the image forming on the photosensitive drum 107 is initiated so that the synchronization between the image forming on the photosensitive drum 107 and the rotation of the intermediate transfer belt 107 is obtained.
However, the above-described procedure for obtaining the synchronization has a drawback in which the synchronization is made in a relatively good condition at the leading side of the images but it is prone to be out of order. As a result, the resultant color toner image is distorted. This is due to the mechanism of the intermediate transfer belt 106. That is, different from the photosensitive drum 107, the intermediate transfer belt 106 receives varying loads of mechanisms for cleaning, discharging, and transferring during a rotation cycle. These mechanisms are switched between two positions to connect and disconnect the intermediate transfer belt 106. In addition, the intermediate transfer belt 106 is supported with a plurality of rollers and each of which may have a manufacturing error and a center displacement. Accordingly, these undesirable factors may irregularly affect the rotation of the intermediate transfer belt 106.
An exemplary measurement result of position variations caused on the surface of the intermediate transfer belt 106 per one rotation is shown in FIG. 2A. It is presumed from this graph that the peak of the variations is at the center in each rotation. FIG. 2B shows the position variations per color. That is, when the color image forming apparatus operates under the conditions as shown in FIG. 2A, the respective color images having the position variations shown in FIG. 2B are overlaying one to another on the intermediate transfer belt 106.
To overcome the above-identified problems, the present invention proposes a novel image forming apparatus. In one exemplary embodiment, the image forming apparatus includes a drum, an optical scanning mechanism, a development mechanism, an intermediate transfer member, a plurality of movement detecting mechanisms, and a controller. The drum is configured to have a photosensitive surface. The optical scanning mechanism is configured to deflect a laser light beam modulated in accordance with image data per color to form a latent image on the photosensitive surface of the drum. The development mechanism is configured to include a plurality of different color toners and to develop the latent image formed on the photosensitive surface of the drum with a corresponding color toner into a color toner image. The intermediate transfer member is configured to be rotated in synchronism with a rotation of the drum and to receive the color toner image multiple times to form thereon a composite color toner image including multiple images of the different color toners overlaying on one another. The plurality of movement detecting mechanisms are configured to detect respective movements of the drum and the intermediate transfer belt. The controller is configured to control respective rotations of the drum and the intermediate transfer belt with results of respective detection being performed by the plurality of movement detecting mechanisms.
The optical scanning mechanism preferably generates a sync signal per line scanning. The drum and the intermediate transfer belt may have respective patterns uniformly spaced on at least one of front and inside side edges of the drum and the intermediate transfer belt. The plurality of movement detecting mechanisms may include respective optical detecting devices configured to detect the respective patterns of the drum and the intermediate transfer belt and to generate respective pattern detection signals. The controller may compare the respective pattern detection signals from the respective optical detecting devices for the drum and the intermediate transfer belt with the sync signal from the optical scanning mechanism, and controls rotation of the intermediate transfer belt and rotation of the drum in synchronism with rotation of the intermediate transfer belt.
The above-mentioned color image forming apparatus may further include a plurality of supporting members configured to drive and support the intermediate transfer belt, and to keep distance from the pattern provided to the intermediate transfer
The above-mentioned color image forming apparatus may further include a cleaning member configured to clean off a surface of the pattern provided to the intermediate transfer belt.
The above-mentioned color image forming apparatus may further include a cleaning member configured to clean off a surface of the pattern provided to the drum.
The above-mentioned color image forming apparatus may further include a discharging member configured to discharge an electric charge from a surface of the pattern provided to the intermediate transfer belt.
The above-mentioned color image forming apparatus may further include a discharging member configured to discharge an electric charge from a surface of the pattern provided to the drum.
Each of the respective patterns provided to the drum and the intermediate transfer belt may be divided into a plurality of short patterns arranged in parallel in at least two rows.
Each of the respective patterns provided to the drum and the intermediate transfer belt may be an integral multiple of an image writing pitch according to a resolution of the optical scanning mechanism.
At least one of the respective optical detecting devices for the drum and the intermediate transfer belt may be arranged at a position close to a position where the drum contacts the intermediate transfer belt.
The plurality of short patterns arranged in parallel in at least two rows may be arranged with space between at least two rows. The patterns are read with a single optical detector which generates a composite detection signal for each of the drum and the intermediate transfer belt, and the controller may control the rotation of each of the drum and the intermediate transfer belt.
The plurality of short patterns arranged in parallel in at least two rows may be arranged in an overlaid manner between at least two rows and with a single pitch and are read with a single optical detector which generates a composite detection signal for each of the drum and the intermediate transfer belt, and the controller may control the rotation of each of the drum and the intermediate transfer belt.
The above-mentioned color image forming apparatus may further include a cleaning mechanism configured to clean a residual toner off of a surface of the intermediate transfer belt. In this case, the pattern provided to the intermediate transfer belt includes a reference base mark. The optical detecting device for reading the pattern provided to the intermediate transfer belt detects the reference base mark and generates a reference base mark signal, and the controller includes a counting circuit configured to count a number of pattern detection signals based on the reference base mark signal. The controller controls a connection and disconnection motion of the cleaning mechanism to the intermediate transfer belt based on the count of the number of pattern detection signals.
The above-mentioned color image forming apparatus may further include a secondary transfer mechanism configured to transfer the composite color toner image formed on the intermediate transfer belt onto a recording sheet. In this case, the pattern provided to the intermediate transfer belt includes a reference base mark. The optical detecting device for reading the pattern provided to the intermediate transfer belt detects the reference base mark and generates a reference base mark signal. The controller includes a counting circuit configured to count a number of pattern detection signals based on the reference base mark signal and controls the secondary transfer mechanism to transfer the composite color toner image formed on the intermediate transfer belt onto a recording sheet.
The above-mentioned color image forming apparatus may further include a registration roller configured to feed a recording sheet towards the intermediate transfer belt in synchronism with a rotation of the intermediate transfer belt. In this case, the pattern provided to the intermediate transfer belt includes a reference base mark, the optical detecting device for reading the pattern provided to the intermediate transfer belt detects the reference base mark and generates a reference base mark signal. The controller includes a counting circuit configured to count a number of pattern detection signals based on the reference base mark signal and controls the registration roller to feed a recording sheet towards the intermediate transfer belt in synchronism with the rotation of the intermediate transfer belt.
The optical detecting device may be arranged at a position at which the intermediate transfer belt is in a horizontal position. The optical detecting device may be further arranged at a position at which a mechanical vibration less occurs.
The above-mentioned color image forming apparatus may further include a damper mechanism configured to reduce mechanical vibrations affecting the intermediate transfer belt.
The pattern provided to the intermediate transfer belt may include a reference base mark. The optical detecting device for reading the pattern provided to the intermediate transfer belt may detect the reference base mark and generates a reference base mark signal. The controller may include a pattern detection counting circuit configured to count a number of pattern detection signals based on the reference base mark signal and a clock signal counter configured to count, based on the reference base mark signal, a number of clock signals having a clock cycle at least shorter than a cycle of the pattern detection signals. The controller may control a rotation of the intermediate transfer belt based on a number of pattern detection signals and a number of clock signals counted during two sequential pulses of the reference base mark signal.
The optical detecting device may use multiple light beams to detect the patterns.
The present invention further describes a novel color image forming method capable of performing precise synchronization between toner image formation per color component and the overlaying of color components. In one example embodiment, the method includes the steps of rotating, deflecting, developing, receiving, detecting, and controlling steps. A first rotating step rotates a photosensitive surface. The deflecting step deflects a laser light beam modulated in accordance with image data per color to form a latent image on the photosensitive surface. The developing step develops the latent image formed on the photosensitive surface into a color toner image with a corresponding color toner from among a plurality of different color toners. A second rotating step rotates intermediate transferring belt in synchronism with a rotation of the photosensitive surface. The receiving step receives the color toner image multiple times to form a composite color toner image including multiple images of the different color toners overlaying one to another on the intermediate transfer belt. The detecting step detects respective movements of the photosensitive surfaces and the intermediate transferring belt. The controlling step controls respective rotations of the photosensitive surfaces and the intermediate transferring belt with results of respective detection performed by the detecting step.
The deflecting step may generate a sync signal per line scanning. In this case, the photosensitive surface and the intermediate transferring belt have respective patterns uniformly spaced on at least one of a front and inside side edges of the photosensitive surface and the intermediate transferring belt. The detecting step detects the respective patterns of the photosensitive surface and the intermediate transferring belt and generates respective pattern detection signals. The controlling step compares the respective pattern detection signals for the photosensitive surface and the intermediate transferring belt with the sync signal from the deflecting step and controls rotation of the intermediate transferring belt and rotation of the photosensitive surface in synchronism with rotation of the intermediate transferring belt.